RESULTS AND CONCLUSIONS

GIS Analysis

For this study, it may appear circuitous to start and end with point
features, but a mix of the points and lines with the dynamic
segmentation model provided the best tools to analyze the data.
Points
and lines do not preserve time-sequential data, but the dynamic
segmentation model falters on query and display speed. The slow query
speed probably is attributable to the sequential nature of the model:
commands such as EVENTLINES and EVENTLINETEXT need to visit the whole
trackline to produce the segments of interest listed in the event
tables (Table 5,
plotrt.aml).
Routes also are disrupted if two
consecutive times have the same location--which could happen if the
survey vessel were stationary; the duplicate records were removed for
these calculations. The format of the measure item in the section
attribute table of the route coverage is limited to 4,12,F,3. We have
worked around this limitation by using only the day, hour, and minute
fields of the time record. However, this limitation needs to be
addressed if
we are to work with surveys that cross year and, soon, century
boundaries for which we will need more significant digits in the time field.

Sea-bottom Sedimentary Processes

The small-scale irregularities in sea-floor morphology and current
directions are easily displayed in the plots derived from the
observation tables. The still photographs reveal that the floor of
Mamala Bay is characterized by morphologies ranging from well-formed ripples to
fairly disorganized sediment surfaces (no ripples evident).
(Figure 6).
There is a broad spectrum of
ripple types, including both symmetrical and asymmetrical forms. In
profile, crests commonly are sharp (although they can be rounded), and
in plan, they are straight to curved and continuous to discontinuous
(Figure 5).
Some ripples appear highly degraded, and others have
crests that are short and disorganized. Ripple type can change
significantly over a short distance (1 minute of time or 20-40 m of
distance, depending on ship speed).

Ripples with discernible asymmmetrical form provide an inferred current
direction; symmetrical ones suggest one of two possible current
directions or an oscillatory current (for example, by waves) with no
net translation. These observations provide a sense of the dominant current
directions in Mamala Bay, but, as with the ripple type, the current
direction may also vary greatly over small distances (Figure 7). The
majority of asymmetrical ripples are short-crested, have a lunate or
linguoid shape, and face upslope or along-slope in a westerly to
northwesterly direction; few face downslope. There are a few areas
over which ripples face consistently to the east.

Supporting data from other aspects of the Mamala Bay study suggest that the
ripples (and larger bedforms) appear to have been formed by episodic
bottom currents, perhaps internal waves (Hampton and others, 1995). The
currents are oscillatory, but they transport dredged material and
native sediment primarily in a net westerly to northwesterly
direction.

The observations from the photographs in conjunction with grain-size
analyses provide "ground-truthing" of the features evident in the
sidescan-sonar image (Figure 2).
As other types of data are analyzed and mapped with tools described
here, a more thorough understanding of the sedimentary processes and,
consequently, the fate of the dredged material in Mamala Bay should
emerge.